Radiation-sensitive camera shutter and aperture control systems

ABSTRACT

A VOLTAGE THAT VARIES LINERALY WITH LIGHT INTENSITY VARIATION IS GENERATED BY AN AMPLIFIER HAVING A DIFFERENTIAL INPUT STAGE CONNECTED TO A LIGHT RESPONSIVE DIODE. TWO HIGH GAIN TANSISTORS ARE INCLUDED IN THE DIFFERENTIAL INPUT STAGE TO PROVIDE AMPLIFICATON OF THE SIGNAL CURRENTS OF THE LIGHT RESPONSIVE DIODE. IN A CAMERA SHUTTER AND APERTURE CONTROL SYSTEM, THE LINEARLY VARYING LIGHT INTENSITY VOLTAGE IS AMPLIFIED TO CONTROL TWO TRESHOLD DETECTOR CIRCUITS. AN INHIBITING CIRCUIT PREVENTS ONE OF THE THREHOLD DETECTOR CIRCUITS FROM RESPNDING TO THE LIGHT INTENSITY VOLTAGE UNTIL THE FIRST THRESHOLD CIRCUIT HAS COMPLETED ITS DESIRED OPERATION.

Jan. 1, 1974 K. E. YEARS Re 27,867

RADIATION-SENSITIVE CAMERA SHUTTER AND APERTURE CONTROL SYSTEMS DriginalFiled May 28, 1970 3 Sheets-Sheet 1 FIG. 2

|00 f o1 E g Z -1 I0 lZJ 3 m I U C FIG. 3 5 Q LU lx. fr u. 0g 1u 01000!U) :1 O E 2 1 1 1 1 1 1 1 :J' O14 O5 (')6 U WAVELENGTH (mrc'oms) Jan. l,1974 Original Filed May 28, 1970 K. E. YEARS RADIATIONSENSITIVB CAMERASHUT'IRR AND AVERTURE CONTROL SYSTEMb- 3 Sheets-Sheet L FIG. 5

FIG. 7

NTRL

K. E. YEARS Jan. l, 1974 SYSTEMS RAI)IAT1G\ ,SENSIT l Vi, CAMLHA SHUTTYHAND AFEHTURE 3 Sheets-Sheet Original Filed May 28, 197C) mmm UnitedStates Patent O 27,867 RADIATION-SENSITIVE CAMERA SHUTTER AND APERT URECONTROL SYSTEMS Kenneth E. Years, Plano, Tex., assignor to TexasInstruments Incorporated, Dallas, Tex.

Original No. 3,626,825, dated Dec. 14, 1971, Ser. No. 41,402, May 28,1970. Application for reissue May 5, 1972, Ser. No. 250,799

Int. Cl. G01j l/00 U.S. Cl. 95-10 C S Claims Matter enclosed in heavybrackets appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE A voltage that varies linearly with lightintensity variation is generated by an amplifier having a differentialinput stage connected to a light responsive diode. Two high gaintransistors are included in the differential input stage to provideamplification of the signal currents of the light responsive diode. In acamera shutter and aperture control system, the linearly varying lightintensity voltage is amplified to control two threshold detectorcircuits. An inhibiting circuit prevents one of the threshold detectorcircuits from responding to the light intensity voltage until the firstthreshold circuit has completed its desired operation.

This invention relates to photosensor control and more particularly tophotosensor control circuitry that produces a voltage varying linearlywith light intensity.

By far the greatest use of light responsive detectors is in circuitrythat produces an on-off signal. When the ambient light in which aphotosensor is located reaches a critical level, the detector circuitswitches from one steady-state condition to a second steady-statecondition. Such circuits usually employ the photosensor in a voltagesensing arrangement. A few circuits are designed to produce an outputvoltage that varies with light intensity; these circuits also employ thephotosensors as a voltage device. Voltage responsive circuits have foundlimited use with photosensors because most detectors produce a voltagevariation that is too small for the conventional arnplifier circuit.

An object of the present invention is to provide an amplifier forgenerating a voltage that varies linearly with light intensity. Anotherobject of this invention is to provide an amplifier including adifferential input stage for producing a voltage that varies linearlywith light intensity. A further object of this invention is to providean amplifier including a photosensor in a current responsiveconfiguration. Still another object of this invention is to provide anamplifier having a high gain differential input stage connected to aphotosensor. A still further object of this invention is to provide anautotilter photosensor in an amplifier for producing a voltage thatvaries linearly with light intensity. Yet another object of thisinvention is to provide a photosensor in a circuit that produces avoltage that varies linearly with light intensity for camera shutter andaperture control.

In accordance with this invention, an amplifier for generating a voltagethat varies in accordance with light intensity includes a lightresponsive diode that produces a current signal that changes with thelight intensity incident thereon connected to a different input section.A feedback loop connected from the output of the amplifier and to oneside of the light responsive diode establishes the closed loop amplifiergain and relates the output of the amplifier to the signal generated bythe diode. In one configuration of a feedback loop, the amplifier outputReissued Jan. 1, 1974 varies linearly with the light intensity incidenton the light responsive diode.

In accordance with a more specific embodiment of this invention, a lightresponsive diode that generates a current signal that varies with lightintensity incident thereon connects to the inputs of a differentialamplifier. The differential amplifier includes a first input transistorwith a current gain factor in the range of from 1000 to 5000 connectedin a differential configuration with a second input transistor alsohaving a current gain factor in the range of from 1000 to 5000. Afeedback loop connected from the output of the amplifier to one side ofthe light responsive diode determines the closed loop amplifier gain andrelates the output of the amplifier to the signal generated by the lightresponsive diode. A biasing source connected to the second input of thedifferential configuration and to one side of the light responsive diodeestabiishes a reference level for amplifier operation.

A more complete understanding of the invention and its advantages willbe apparent from the specification and claims and from the accompanyingdrawings illustrative of the invention.

Referring to the drawings:

FIG. 1 is a schematic of a bipolar differential amplifier having anoutput that varies proportionately with the light intensity as measuredby a photosensor;

FiG. 2 is a cross section of a near infrared auto-filter p-n junctionphotosensor;

FIG. 3 is a curve of relative luminosity as a function of wavelength inmicrons;

FIG. 4 is a plot of photocurrent as a function of voltage for a p-njunction photosensor;

FIG. 5 is a schematic and block diagram of' a camera aperture andshutter control system employing the differential amplifier of FIG. 1;

FIG. 6 is a schematic of a bipolar transistorized circuit for a cameraaperture and shutter control system; and

FIG. 7 is a schematic of an MOS circuit producing an output that variesproportionately with the light intensity incident on a photosensor.

Referring to FIG. 1, a photosensor 10 in a diode configuration has acathode electrode connected to the base electrode of a first inputtransistor l2 and an anode electrode connected to the base electrode ofa second input transistor 14. A bipolar circuit of the type shownexhibits high voltage gain per stage and accurate light level sensingincident on the photosensor 10. To accommodate the iow current levels ofthe photosensor 10, the transistors 12 and 14 have a super-betacharacteristic. A superbeta transistor is defined as one with electricalcharacteristics of: =1000 to 5000 and BVCEO of approximately 2 to 5volts. The base widths of super-beta transistors are nominallyapproximately 0.01 mil. Because of the high beta values, the effectiveinput impedance of the bipolar transistor amplifier of FIG. 1 is afactor of 10 above an amplifier using conventional beta transistors atthe input stage.

To maintain the 2 to 5 volt BVCEO value for the transistors 12 and 14,the circuit of FIG. l include transistors 16 and 1S. Transistor 16 has abase electrode connected to the emitter of the transistor 12 and acurrent source 20. Additional circuitry for maintaining the current andvoltage level for the transistor 12 includes a pair of back-to-backtransistors 22 and 24 along with a current source 26. Transistor 18 hasa base electrode connected to the emitter of the transistor 14 and acurrent source 28. Additional circuitry for maintaining the current andvoltage level of the transistor 14 includes a transistor 30 connected ina back-to-back arrangement with a transistor 32 and a current source 34.Not included in the schematic of FIG. l are various resistors forestablishing biasing and current levels. The circuit of FIG. l isenergized from a D.C. voltage source connected to the terminal 36.

A differential output from the transistors 12 and 14 appears at theoutput terminals 38 and 40 and is proportional to the light intensityincident on the photosensor 10.

With the diode connected as shown, it operates in a current mode; thatis, the transistors l2 and 14 respond to current levels generated in thediode. In the current mode of operation, a higher frequency response isachievable from the diode 10 as compared to a voltage mode of operation.This advantage of current mode operation is due to the capacitanceassociated with the photodiode. In a voltage mode of operation, thiscapacitance must be charged and discharged. Diode capacitance has littleif any affect in the current mode.

In one form, the photosensor 10 is a selenium photovoltaic diodeconstructed by depositing a layer of selenium on a conductive substratefollowed by a layer of cadmium oxide. The N-type CdO forms a junctionwith the ptype selenium. Photons penetrate the opaque CdO layer andcreate hole-electron pairs in the selenium. The electrons slide down thep-junction potential barrier into the CdO and a current proportional tothe light created hole-electron pairs will flow and be amplified by thetransistors l2 and 14.

In applications where light memory (the retention of the hole-electronpairs in the selenium) is of concern, an all silicon photosensor ispreferred to the thin film sclenium junction photosensors. Siliconphotosensors exhibit improved signal-to-noise ratio over the seleniumcounterpart and silicon is memory free for response times greater than afew milliseconds.

Referring to FIG. 2, there is shown in cross section a siliconphotosensor 10 having a silicon substrate 42 as the collector electrodewith a base region 44 and an emitter region 46 that are diffused intothe substrate by subsequent diffusion processes through a silicondioxide layer 48. Silicon p-n junctions will respond readily to both thevisible (0.4 to 0.7 micron) and the near infrared (0.7 to l.l microns)wavelengths because of the nature of the silicon photo absorptioncoeficient.

To render the silicon photosensor insensitive to the near infrared forapplications where only visible light is f of interest, selective photoresponse is achieved by arranging the transistor diffusion schedule suchthat the deeply penetrating near infrared radiation produces ionizationin the transistor collector body where the resulting photocurrent isinoculously removed by short cirf cuiting the collector-base junction.This shorting is accomplished by the jumper wire 50. For the nearinfrared radiation photons to travel through the emitter and basediffusions into the collector region, the depth of the base region is onthe order of S microns. Using a 2 micron. diffusion for the emitter 46,and the 8 micron diffusion for the base region 44, photons in thevisible region will penetrate through the emitter region into the baseregion where they produce photocurrents related to the photobombardment.

The photosensor 10 of FIG. 2 will be connected into the amplifier ofFIG. 1 such that its emitter-base junction is zero or slightly reversebiased. With the photosensor so connected and with the collector-basejunction physically short circuited by the jumper wire S0, little if anytransistor action will take place.

By operating the silicon photosensor with the emitterbase junction in azero or a slightly reverse biased configuration, the dark currentleakage characteristic of a p-n junction, which is temperaturedependent, may be eliminated. The leakage current for a p-n junction atvoltages less than a few tenths volts positive is given by:

IDmk=In (enkt-1)+ISurf.+IGen. (dep. layer) (l) Each of the currents inEquation 1 is [are] strongly temperature dependent and will introduce anerror in the photo generated current of the diode since the totalcurrent flow with the diode exposed to illumination (assuming thedepletion layer width is zero) will be:

ITMFIDark-QRU-niI-p) (2) where R=carrier generation rate per unit volumeof incident illumination, and

Ln. Lp:ditfusion length of minority carrier electrons and holes,respectively.

With the emitter-base junction operated at a zero or slightly negativebias, Equation 2 reduces to:

whereby temperature dependent leakage current components have beeneliminated. The zero or slightly negative bias mode of operation isgraphically illustrated by the curves of FIG. 4 by points A1, A2 and A3which represent illumination intensity L1, L2 and L3, respectively.

To limit the response of a silicon photosensor [below] to the visibleregion, an optical filter 52 is placed in the path of the radiationincident on the sensor, as illustrated in FIG. l.

Referring to FIG. 3, there is shown a luminosity curve, that is. thesensitivity of the human eye to radiant energy as a function ofradiation wavelengths. By employing a selective diffusion schedule asexplained and the optical filter 52, the response of a siliconphotosensor may be limited to the visible region between 0.4 and 0.7micron.

One application of the circuit of FIG. l, using either a seleniumphotovoltaic diode or a. silicon photosensor, is in a camera shutter andaperture control as illustrated in FIG. 5. The photosensor 10 generatesa current tiow in the input stage of an operational amplifier 54 inaccordance with light intensity passing through the optical filter 52.The differential amplifier of FIG. l comprises the input stage of theoperational ampiificr S4. A voltage output from the amplitier 54 isproportional to the light intensity on the photosensor 10 and is appliedto the input of an operational amplifier 56 through an adjustableresistor 58.

A feedback circuit connected from the output of the amplifier 54 and tothe cathode electrode of the photosensor 1I] tailors the input of theamplifier 56 to have a desired relationship to the light intensity. Thisfeedback circuit includes two paths selectable by means of a switch 60.In the position shown, switch 60 connects a resistor 62 in the feedbackcircuit and the output of the amplifier 54 varies proportionally withthe light intensity incident on the photosensor 10. With the switch 60in the second position, the feedback circuit includes a variableresistor 64 and a capacitor 66. This circuit relates the output of theamplifier 54 to the time integral of the current generated by thephotosensor 10. A switch 68 is closed to shunt the capacitor 66 at thecompletion of one operating cycle of the control system of FIG. 5.

A signal applied to the input of the operational amplifier 56 isamplified therein to an output voltage level appearing at a terminal 70.A voltage at the terminal 70 is fed back to the input of the amplifier56 through a feedback resistor 72 and divided in a voltage dividernetwork of resistors 74, 76 and 78 into two threshold detector inputsignals. A voltage at the junction of resistors 74 and 76 is applied toan input of a threshold detector driver 80 through a timing circuitconsisting of a capacitor of a capacitor SZ and a resistor 84. An outputof the driver -80 connects to a solenoid 86 for controlling the openingof a camera aperture 88 through a mechanical linkage 90. An output ofthe driver 80 is also applied to an inhibit circuit 92 that interruptsthe circuit between the junction of resistors 76 and 78 and the inputterminal of a threshold detector driver 94.

Initially, the aperture 88 begins to open and at the same time theswitch S-3 is opened. This operation continues until a charge on thecapacitor 82 reaches a threshold level. At the threshold level, theoutput voltage at the output of the driver 80 drops to zero, therebydeenergizing the solenoid 86. This clamps the aperture [aperature] 88 ata desired setting. Since the output of the amplifier 56 at terminal 70is related to the output of the amlifier 54, which in turn is related tothe light intensity incident on the photosensor 10, the opening theaperture 88` will be determined by the level of light intensity passingthrough the optical filter 52.

Upon completion of the operation of the driver 80, the inhibit circuit92 completes the circuit between the junction of resistors 76 and 78 andthe input of the threshold detector driver 94. A voltage appearing atthe junction of the resistors 76 and 78 is applied to the driver 94 toactuate a solenoid 96 for controlling the operation of a camera shutter98 through a mechanical linkage 100. Also, upon completion of theoperation of the driver 80, the switch 60 is changed to a position toconnect the capacitor 66 in the feedback circuit of the operationalamplifier 54. The output of the amplifier 54, and consequently theoutput of the amplifier 56 at terminal 70, now varies as the timeintegral of the light intensity incident upon the photosensor 10. Thissignal changes in a manner determined by the resistor 64 and thecapacitor 66. When it reaches a threshold level as determined bycircuitry of the detector driver 94, the output of the driverde-energizes the solenoid 96 to return the shutter 98 to a closedposition. Thus, the time that the shutter 98 remains open is dcerminedby the light intensity incident on the photosensor 10. Note, that bymeans of the inhibit circuit 92, operation of the shutter 98 isprevented until after the aperture 88 has been opened to the desiredlevel.

Many threshold detectors may be used in the system illustrated and mayconsist of a high gain differential input and a single ended outputamplifier. The function ofthe detector drivers is to compare a signalvoltage on one input with a fixed internal reference. When the inputexceeds the reference voltage, the output amplifier is switched to anon-conducting state thereby changing the energization State of therespective solenoid.

Referring to FIG. 6, there is shown the complete schematic of a cameraand shutter control system including the photosensor coupled to adifferential amplifier input stage of super-beta transistors 102 and104. The cathode electrode of the photosensor 10 also connects to abiasing circuit comprising resistors 106 and 108 and a variable resistor110. A reference voltage, as established at the output of a referencesupply 112, is applied to the anode electrode of the photosensor 10 andthe base electrode of the transistor 104.

The reference supply 112 includes a differential amplifier oftransistors 114 and 116 having a comomn emitter connection. Emittercurrent for the transistor pair is established and controlled by anetwork consisting of a resistor 118 and a transistor 120. The referencevoltage generated by the supply 112 appears at the emitter terminal of atransistor 122 having a base electrode connected to the collectorelectrode of the transistor 116. Resistors 124 through 127 establish thevarious bias voltage levels and current levels for operation of thetransistors of the reference supply 112.

To protect the super-beta transistors from over-voltage surges, atransistor 128 is shunted across the transistor 102 and a transistor 130shunts the transistor 104. Collector current control for the transistors102 and 104 is provided by a circuit that includes a transistor 132 andresistors 134 i through 138. Transistor 132 is connected to the positiveside of a D.C. supply at terminal 140` through the resistor 134. Theemitter circuit for the transistor 102 includes a transistor 142 havinga base electrode connected to the junction of resistors 144 and 146 andan emitter electrode connected to ground through a resistor 148.Similarly, the super-beta transistor 104 includes a transistor 150 inthe emitter electrode circuit with the base electrode of the transistorconnected to the junction of resistors 144 and 146 and having an emitterelectrode connected to ground through a resistor 152. A voltagedeveloped at the junction of the resistors 144 and 146 is established bytransistors 154 and 156 along with resistors 158 and 159 in a circuitconnected from the D.C. supply to ground.

The output circuit for the transistor 102 includes transistors and 162in addition to the transistor 128. The emitter current of the transistor162 is controlled by a resistor 164, and the emitter current of thetransistor 160 and the base drive of the transistor 162 are [is]controlled by a resistor 166. This voltage at the emitter electrode ofthe transistor 160 also drives a transistor 168 in the output circuitfor the transistor 104. A voltage at the collector electrode of thetransistor 168 is the output of the differential input pair and isapplied to cascaded transistors 170 and 172 that are part of a circuitthat contains a base drive resistor 174 and a capacitor 176.

Connected to the common collector junction of the transistors 170 and172 is the base electrode of a transistor 178 and the collectorelectrode of a transistor 180. Transistor 178 further amplifies theoutput voltage of the differential input pair. Transistor 180, which hasan emitter electrode connected to the positive terminal of a D C. supplythrough a resistor 182, establishes the base bias level of thetransistor 178. Further amplification of the signal from thedifferential input pair is provided by the transistor 184 having a baselevel set by the resistors 186 and 188. The final amplification stage ofthe amplifier 101 in the system shown includes a transistor having abase electrode coupled to the emitter electrode of the transistor 1184.In the emitter circuit of the transistor 190 is a resistor 192 connectedto the D.C. supply.

By operation of the super-beta transistors 102 and 104 and the variousother amplification stages, the voltage at the emitter electrode of thetransistor 190 varies in a predetermined relationship with the lightintensity incident on the photosensor 10. This voltage is coupled to theinput of an operational amplifier 194 and to one of one of' two feedbackcircuits through an electronic switch 196. Switch 196 includestransistors 198 and 200 for determining the initial state of theswitching circuitry. Transistor 198 is coupled to the reference supply112 through the base electrode and the output of a threshold detector202 through a resistor 204 to the emitter electrode. Transistor 200connects to the base electrode of a switching transistor 206 thatconnects a capacitor 208 in the feedback loop for the amplifier 101 whenin a conducting state. Transistor 200 also controls the switchingtransistor 210 through an inverting transistor 21.2. Transistor [200]210 connects resistors 214 and 216 in a feedback loop for the amplifier101. In addition to the transistor 212, the circuit for controlling theoperation of the switching transistor 210 includes transistors 218 and220. Transistor 218 is controlled by the output of the thresholddetector 222 through a base electrode connection.

During a reset cycle of the camera control, a voltage at terminal 224controls the conducting state of transistors 226, 228 and 230 in theelectronic switch 196.

As explained, a voltage at the emitter electrode of the transistor 190is the input to the amplifier 194. This voltage is applied to the baseelectrode of a transistor 232 of a differential pair that includes atransistor 234. The output of this differential pair is determined bythe difference between the voltage at the base electrode of transistor232 and the base electrode of transistor 234. A voltage at the baseelectrode of the transistor 234 is established by the resistor 236connected to the output of the reference supply 112.

Emitter eurent for the transistors 232 and 234 is controlled bytransistors 238 and 240, respectively. The

base electrode of each of these transistors is connected to thecollector electrode of transistor 120 of the reference supply 112.Resistors .242 and 244 connected to the emitter electrodes of thetransistors 238 and 240, respectively, complete the current emittercontrol circuitry for the transistors 232 and 234. Collector current ofthe transistor 232 is established by a transistor 246 having an emitterelectrode connected to the terminal 140 and a base electrode to the baseeicctrode of a transistor 248. Transistor 248 is connected in thecollector electrode circuit of a transistor 250 which along with atransistor 252 controls the base curent of the transistor 246.

An output transistor 254 of the amplifier 194 has a base electrode tiedto the collector electrode of the transistor 232 and to a filteringcapacitor 256. The emitter control circuit for the transistor 254includes resistor 260.

The output voltage of the amplifier 194 as appearing at the emitterelectrode of the transistor 254 is fed back to the base electrode of thetransistor 232 through a feedbaclr resistor 262. Resistor 262 along withthe input resistor 264 establishes the external gain of the amplifier194.

The output of the amplifier 194, which corresponds to the output of theamplifier 56 of HG. 5, connects to the input ot the threshold detector202 and an inhibit circuit 266. The threshold detector 202 correspondsto the detector driver 80 of FIG. 5. An output Voltage from theamplifier 194 is coupled through a timing network of a capacitor 268 anda variable resistor 270 to the base electrode of a transistor 272.Transistor 272 is connected in a differential amplifier configurationwith a transistor 274. These two transistors have a common emitterjunction connected through a resistor 276 to ground. The output of thedifferentially connected transistors 272 and 274 is the differencebetween the voltage connected to the base electrode of the transistor274 and the voltage at the emitter electrode of the transistor 254. Thisoutput voltage appears at the collector electrode of a transistor 280having a base electrode tied to the collector of the transistor 272.Resistors 282 and 284 establish the current levels for the transistors272 and 280.

A resistor 286 connected to terminal 140 and resistor 278 which is tiedto the output of the source 112 estabfishes the base drive for thetransistor 274 and the base drive for the transistor 288. Transistor 288establishes the collector current for a transistor 290 having a baseelectrode tied to the collector electrode of the transistor 280. Avoltage at the collector of the transistor 290 is applied to the emitterelectrode of the transistor 198 of the electronic switch 196 and to aresistor network of resistors 292, 294 and 296.

The voltage at the junction of resistors 294 and 296 drives a.transistor 298 in an output stage of the threshold detector 202.Transistor 300 comprises the final output stage of the detector 202 andenergizes the aperture solenoid 302 to control the opening of a cameraaperture.

Returning to the output of the amplifier 194 as appearing at the emitterelectrode of the transistor 254, this voltage is also applied to thebase electrode of a transistor 308 in the threshold detector 222.Transistor 308 is part of a differential pair that includes a transistor310 having a base electrode voltage determined by the setting of avariable resistor 312. An output signal from the dierential pair appearsat the collector electrode of a transistor 314 having a base electrodeconnected to the collector electrode of the transistor 308. Resistors316 and 318 establish the current levels for the transistors 308 and314.

The threshould detector 222 is similar in many respects to the thresholddetector 202. One dierence, however, is a flash control provision thatincludes differential transistors 320 and 322. The base electrode oftransistor 322 is driven by the output of the reference supply 112. Thebase electrode of the transistor 320 is coupled to a timing circuit of aresistor 324 and a capacitor 326.

Emitter current for the differential transistors 308 and 310 iscontrolled by a transistor 328 having a base electrode coupled to thecollector electrode of a transistor 330 in the inhibit circuit 266. Thecollector electrode of the transistor 328 is tied to the emitterelectrode of a transistor 332, also in the inhibit circuit 266. Thus,transistor 328 establishes the emitter current for the transistors 308and 310 through a resistor 334, and, bythe interconnection to theinhibit circuit 266, controls the operation of the differentialtransistors 308 and 310.

When in the inhibit state, the detector 222 is in a hold condition. Thiscontinues so long as the aperture solenoid 302 operates to position thecamera aperture. After the aperture has been set, as determined by asignal at the base electrode of the transistor 304, the output voltageon the transistor 314 is applied to the base electrode of a transistor336. A collector bias for the transistor 336 is provided by means of atransistor 338 having a base electrode tied to the Wiper arm of thevariable resistor 312. The voltage at the variable resistor 312 isestablished by the output of the reference supply 112 and transistors340 through 343 and resistors 344 through 346.

A voltage appearing at the collector electrode of the transistor 336 isapplied to a network of resistors 348, 350 and 352. At the junctionbetween resistors 350 and 352 there is connected the base electrode of atransistor 354 of the output stage of the threshold detector 222. Atransistor 356 is also included in the output stage and has an emitterelectrode coupled to ground through a resistor 358. In series with thecommon connection of the collector electrodes of transistors 354 and 356is a shutter control solenoid 360 that has one terminal tied to thepositive side of a D.C. supply at a terminal 362.

As mentioned, the operation of the threshold detector 222 is inhibitedby the inhibit circuit 266. A voltage at the emitter electrode of thetransistor 300 drives a transistor 304 through a resistor 306 in theinhibit circuit. In addition to the other transistors previouslydefined, the circuit 266 further includes transistors 364 and 366 eachhaving a base connection to the collector electrodes of transistors 332and 304, respectively. The remainder of the inhibit circuit 266 includesresistors 368 through 373. This circuit operates to inhibit thethreshold detector 222, as explained with regard to the system of FIG.5.

The operation of the circuit of FIG. 6 is similar to the system of FIG.5. The capacitor 268 and resistor 270 determine the operation of theaperture control solenoid 302 in conjunction with the light incidentupon the photosensor' 10. Upon completion of the aperture settingoperation, the feedback capacitor 208 is connected in the feedback loopfor the amplifier 101 and the inhibit circuit 266 controls the shuttersolenoid 360, leaving the camera shutter open for a time determined bythe amount of light incident upon the photosensor 10.

In addition to bipolar circuitry, the photosensor 10 may be included inthe input stage of a P-channel MOSFET differential amplifier asillustrated in FIG. 7. The photosensor l0, which receives light throughthe optical filter 52, connects to the [base] gate electrode offield-effect transistors 374 and 376. These transistors are coupled in adifferential amplifier configuration with a common connection through atransistor 378 for [emitter] source current control; the [emitter]source current being established by the setting of a variable resistor380. The [collector] drain current for the transistors 374 and 376 iscontrolled by transistors 382 and 384, respectively, having oneelectrode coupled to the negative terminal of a DC. supply at terminal386. An output signal from the transistor 374 is applied to a transistor388 which comprises part of a differential pair that includes atransistor 390 coupled to the output of the transistor 376. Transistors388 and 390 have a common connection to a transistor 392 that controlsthe current flow through these transistors. Additional circuitry for thetransistors 388 and 390 includes transistors 394 and 396.

An outuput voltage from the circuit of FIG. 7 appears at the terminals398 and 400 and is related to the light intensity incident upon thephotosensor 10. The differential amplifier configuration of FIG. 7 isincluded in a MOS shutter control circuit in a manner similar to thatdescribed above with respect to the bipolar circuit of FIG. 1.

While several embodiments of the invention, together with modificationsthereof, have been described in detail herein and shown in theaccompanying drawings, it will be evident that various furthermodifications are possible without departing from the scope of theinvention.

What is claimed is:

1. In a camera shutter and aperture control system, the combinationcomprising:

a light-responsive photosensor generating a current signal that varieswith light intensity incident thereon,

an amplifier including a differential input section connected to saidlight-responsive photosensor and having a first feedback loop forrelating the amplifier output proportionately to the diode-generatedsignal and a second feedback loop for relating the amplifier output tothe time integral of the photosensor generated signal,

switching means for connecting each of the feedback loops separately tosaid amplifier output,

a second amplifier having an output that varies with [film speed and]the output of said first amplifier,

a first threshold detector `responsive to the output of said secondamplifier when said switching means connects the first feedback loopacross said first amplifier for controlling the camera aperture setting,

a second threshold detector responsive to the output of said secondamplifier when said switching means connects the second feedback loopacross said first arnplier for controlling the camera shutter operation,and

means for inhibiting the operation of said second threshold detectoruntil said first threshold detector sets the opening of the cameraaperture.

2. In a camera shutter and aperture control system as 10 set forth inclaim 1 including timing means connected between the output of saidsecond amplifier and said first threshold detector for controlling theoperation of said first detector in accordance with the output of thesecond amplifier.

3. In a camera shutter and aperture control system as set forth in claim2 including means for biasing the second input to the differentialsection of the first amplifier and one side of said light-responsivephotosensor at a reference level.

4. In a camera shutter and aperture control system as set forth in claim3 wherein said light-responsive photosensor is a selenium photovoltaiccell.

5. In a camera shutter and aperture control system as set forth in claim3 wherein said light-responsive photosensor is a silicon transistor.

6. In a camera shutter and aperture control system as set forth in claim5 including means for shunting the collector-base junction of saidtransistor.

7. In a camera shutter and aperture control system as set forth in claim6 including means for biasing the emitter-base junction of saidtransistor.

8. In a camera shutter and aperture control system as set forth in claim7 including an optical filter to limit the response of said transistorto radiant energy in the visible region.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,349,678 10/1967 Sukuki et al. 95-10 C 3,430,1062/1969 McDowell 250-214 X 3,450,015 6/1969 Reimann et al. 95-10 C3,460,450 8/1969 Ogihara 95-10 C 3,464,332 9/1969 Davison et al 95-10 CJAMES W. LAWRENCE, Primary Examiner U.S. Cl. X.R.

Z-211 J, 214 P; 307-311, 330, 126

